1. Field of the Invention
The present invention relates to an image forming apparatus capable of drawing, from an external apparatus, print data stored therein and executing a print job for the print data, and relates to a control method for the image forming apparatus.
2. Description of the Related Art
Some of multi-function peripherals having multiple functions, such as a printer function and a scanner function, has a hard disk unit (HD) for storage of print data. Print data stored in the HD of such a multi-function peripheral (hereinafter referred to as the first MFP) can be printed by a second MFP having a memory for temporary storage of print data. This type of printing is called pull print. To perform the pull print, the second MFP draws print data from the first MFP and temporarily stores the print data until completion of printing the print data. Thus, it is not essentially required for the second MFP to have an HD.
During the execution by the second MFP of a print job for the print data drawn from the first MFP, another job is sometimes generated. If the other job (hereinafter referred to as the interruption job) has higher priority than the currently executed print job, the currently executed print job is interrupted. At that time, if free space in the memory is less than the memory capacity required for execution of the interruption job, the print data in the memory is erased to ensure the required memory capacity. Upon completion of the interruption job, the second MFP draws again from the first MFP the print data for the interrupted print job and restarts the interrupted print job.
However, the print data is sometimes altered in the first MFP by another user before the print data is drawn therefrom again by the second MFP. In that case, the second MFP cannot acquire the print data before being altered and cannot correctly restart the interrupted print job.
To eliminate this problem, the following two methods are known.
The first method is to prohibit the print data (original) from being altered during execution by the second MFP of a print job for the print data drawn from the first MFP. With this method, it is ensured that the print data drawn again is the same as the initially drawn print data, whereby the same print job can be restarted.
The second method is to save print data stored in the memory of the second MFP to another location on a LAN when an interruption job is generated (Japanese Laid-open Patent Publication No. 2007-30252). With this method, the saved print data can be drawn after completion of the interruption job and the same print job as the interrupted print job can be restarted.
However, according to the first method, print data cannot be altered by the first MFP during execution of the print job for the print data drawn from the first MFP, which is inconvenient for users.
With the second method, since print data is saved from the second MFP to another location via a network such as LAN, it takes much time to save the print data and unnecessary load is applied to the network.